My feet measure 14.5, so usually I wear a 15, or a large fitting 14. I have an average-to-narrowish-side sized foot. & I just went through all this about 3 or 4 months ago. I am "breaking in" kenetrek mtn extremes right now.
Crispi makes 1 model that's a 15, I think it was the Nevada, but I don't remember. I ordered them straight through Crispi and ended up returning them because they were way too roomy in the heel box for me, even with aftermarket thicker soles. Fantastic customer service from them with finding a pair in stock and the return. Length size seemed spot on for a 15.
Hanwag offers 1 model in 15. I haven't tried that one.
Kenetrek offers mtn extreme, and hardscrabble in size 15, both seemed spot on for a 15 in length. I didn't try a 14 in these. These fit best overall out of all I had tried. Minimal break in for me, but I'm a big guy. I'm probably on mile 30 or 40 if we include 18" step ups a couple times a week. Probably closer to 25 trail miles. Sometimes it's difficult to get my heel locked in, & I notice it only when I start doing step ups/steps/very vertical hiking. But these locked my heel in best. Also, I tried both and preferred the mtn extremes more than the hardscrabbles. But both are super nice.
Schnees has at least the Beartooth and granites that are offered 15. I tried the Beartooths & they looked the nicest out of what I tried. I wanted these to work but they were just too tight around my foot, and probably fit length wise like what I imagine a 14.5 would fit like. I spoke with their CS and they said I might have a full profile foot (something like that). Returning them was also very easy. Incredible customer service with these guys as well.
I have a pair Salomon 3d gtx in size 14 that fit like gloves. I would say they fit like a big 14.5, but definitely not 15 in length. I can't wear 2 pairs of socks in those unless they're both thin profile socks. But there is no heel slip in those. They have a little flex and they're a little soft soled compared to the other boots I've mentioned. But the fit is perfection for my foot. The kenetreks allow a little heel slip with me no matter what I do, but it's a tolerable amount.
Also have an older pair of Danner MTN 600s in size 14. I couldn't wear liner socks and thick wool socks in those, but fit length wise with 1 pair of wool socks on. They fit me like they are spot on like what I think a 14.5 would fit like. These feel like outdoor heavy duty basketball shoes compared to the other boots I've tried. Very soft soled and almost cushiony. I don't wear these much anymore. I reach for the Salomons for whatever I would wear these for now.
I really prefer the stiffer profile of the Kenetreks to the softer Salomons, which I didn't think I would. If I could combine the fit of the Salomon to the beefiness of the Kenetreks, my search would be over.
Every pair of feet are different. While I now prefer the stiffer boots, I could easily see how people wouldn't like the stiffness. So it really is best to try a bunch on and walk up some stairs or up and down inclines to be sure they work.
Also, I recommend shopping around at places that offer free returns. Some places cover the return shipping and some don't, but both offer "free returns" so just check each sites policy because shipping costs for boots this big aren't exactly cheap. Especially if you're trying a bunch of different boots to find what you like.
Everyone reading this knows it's frustrating AF trying to find stuff in stock online. Especially when there's <1% chance of finding these in our size at a storefront to try on (unless you live near the manufacturer).
I hope my recent experience with this helps at least some.
Good luck with the search!